FAQ:Should I use a holdingdisk when the final destination of the backup is a virtual tape?
This article answers a FAQ (frequently asked question).
Holding disks and vtapes serve a complete different purpose: holding disk allows different clients to backup simultaneously and the server collects the incomplete images in the holding disk. When a backup image is complete, the server then adds it to the tape queue. The taper can choose the best file, depending on the criteria you set in "taperalgo". Especially "taperalgo largestfit" is helpful fitting as much as possible on a vtape. (e.g. when you want to burn the backups to a DVD later).
- Holding disks allow paralellism and vtapes do not allow it by default (It can be configured to do paralellism).
- Holding disks and vtapes should never be on the same hard disk.
- Use Holding disks if it is faster than the vtapes , eg. Holding disks on SSD or vtapes on USB.
To get parallel dump to vtape, add the following in the storage section:
taper-parallel-write 10 max-dle-by-volume 1
In case there are problems with your vtapes (e.g. the external disk with vtapes is full, or got disconnected), then Amanda can still fall back to degraded mode, and dump only incrementals to the holding disk.
Credit
Based on text by Stefan G. Weichinger, November - December, 2003, with updates in April, 2005. Updates in January, 2018 by Jean-Louis Martineau
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